3D Octant cube model from Rubik's Cube 2x2
Initially I thought about adapting an already existing 3D model of a Rubik's cube but after speaking with a Blender user, he told me that in order to achieve this I just need to:


  3 planes, turn 90° each other, subdivide each, assign material, join.
  Then extrude verts (with Ctrl) and fill.


(so basically he told me to not consider adapting the model because this is something easy)

This was the result he got, which is exactly what I wanted - it misses only the axis and text:



With his message, managed to create the planes (by pressing Shift+A and select Plane from the drop-down list and then rotating them (Plane has rotation 0, 0 0; Plane 001 has rotation 90, 0, 0; Plane 002 has rotation 90, 0, 90)), subdivide each (Tab > Right Click > Subdivide once), and assign a color in Material Properties (notice that to see the colors one has to activate Viewport shading). Then, joined the planes and extruded vertices (Editor mode, right click > extrude vertices and use CTRL do get the point fixed in the proper location).

This is the final result:

Object mode:


Editor mode: